This invention relates to a high-pressure rubber hose which has a reinforcing layer embedded therein, has at least an outer layer thereof formed of a vulcanized ethylene-.alpha.-olefin-diene copolymer rubber (hereinafter referred to as "EPDM" for short), and is adapted to be used as fastened by staking to a sleeved joint. As examples of uses found for this high-pressure rubber hose, there may be citted hoses for the hydraulic system such as a brake hose and a clutch hose, hoses for the air system, and hoses for the coolant system.
In most brake hoses, their outer layers have been formed of a vulcanized CR (chloroprene) rubber or a vulcanized CR-EPDM blend rubber (Japanese Patent Publication No. SHO 59(1984)-36,158). Recently, growth of engine output and adoption of turbo engines have compelled brake hoses to be used under increasingly harsh conditions. In the meantime, the desirability of developing brake hoses which require no maintenance has been finding growing recognition.
Neither the CR rubber not the CR-EPDM blend rubber mentioned above has been capable of acquiring an ability to resist dynamically the action of ozone to a point where the obviation of the necessity for maintenance is realized (Table 1).
It has been proposed to form the outer layer of a brake hose, for example, with a vulcanized rubber of EPDM which excels in dynamic resistance to ozone, resistance to heat, and resistance to weather conditions (Japanese Patent Application Laid-open No. SHO 55(1980)-2,805). Unfortunately, none of the EPDM species heretofore proposed to the art is capable of retaining compression-proof permanent set indispensable to the sealing property and, at the same time, manifesting such mechanical properties such as tensile strength (T.sub.B), tear strength (T.sub.R), and volume relaxation fracture to advantage (Comparative Experiment in Table 1). When such an EPDM rubber hose is fastened by staking to a sleeved joint, for example, it has the possibility of sustaining breakage in the staked end after thermal aging. Thus, the conventional EPDM rubber has failed to meet the need for obviating the required maintenance.